Is anywhere aware of an open source 2D hex tile SDK or engine? I know there are tutorials for developing such a beast, but I want to skip that and go straight to experimenting? Preferably one based on OpenGL.

(The shown map uses a diamond shaped grid for the tiles, but as you can see there is a hex grid that's used for objects at this map. But you can use the hex grid for tiles too, so it is NOT limited to objects.)